Design and analysis of an open-ended waveguide probe for material characterization

Nondestructive evaluation of stratified (layered) composite structures at microwave and millimeter wave frequencies is of great interest in many applications where simultaneous determination of the complex dielectric properties and thicknesses of multiple layers is desired. Open-ended rectangular waveguide probes are effective tools for this purpose. The technique requires a full-wave electromagnetic model that accurately calculates the complex reflection coefficient as a function of frequency and material properties. Subsequently, this information is used in conjunction with the measured complex reflection coefficient to evaluate the sought for material properties. This thesis presents simulated and measured data to investigate the influence that measurement system noise, which contaminates the measured complex reflection coefficient, has on estimating material properties. It will be shown however, that the foremost contributor to errors in estimating material properties is not due to system noise, but rather, is due to an inconsistency between the electromagnetic model and the measurement setup. More specifically, the electromagnetic model assumes an infinite waveguide flange while measurements are conducted using a finite-size flange. Consequently, the results of the model and those from measurements may not be sufficiently alike for accurate dielectric property and thickness evaluation. The work presented here investigates the effect of using an open-ended waveguide with a standard finite-sized flange on the error in evaluating the complex dielectric properties of a composite structure. Additionally, the design of a novel flange that markedly reduces this undesired effect by producing very similar electric field properties, at the flange aperture, to those created by an infinite flange will be presented and verified in measurement --Abstract, page iii

Waveguide Probe for Nondestructive Material Characterization

An open-ended waveguide probe including a finite flange extending outwardly and functioning as an infinite flange. A signal source provides a microwave signal to the waveguide, which in turn transmits microwave electromagnetic energy incident upon an object to be tested. The finite flange at the waveguide\u27s aperture is shaped to reduce scattering of the electromagnetic field reflected from the object and received by the aperture. The probe is adapted for coupling to a receiver for sampling the reflected electromagnetic field received by the aperture and the receiver is adapted for coupling to a processor for determining at least one material characteristic of the object based on sampled electromagnetic field reflected from the object

Finite Flange Correction for Microwave and Millimeter-Wave Nondestructive Material Characterization

Open-ended waveguide material characterization is an effective nondestructive testing (NDT) technique for evaluating the dielectric constant and thickness of individual layers in a multilayered composite structure. A limitation of this technique is that the finite flange contributes to the estimation error, depending on the thickness and dielectric loss factor of the layers. Its effects are non-negligible in particular when measuring the dielectric constant of low-loss and thin materials. This paper studies the effect of using a common finite-flanged open-ended waveguide on the error in estimating the permittivity and loss-tangent of a dielectric sheet. This paper also presents a proposed modification to the flange geometry in order to markedly reduce this undesired effect

Modified Waveguide Flange for Evaluation of Stratified Composites

Nondestructive evaluation of stratified (layered) composite structures at microwave and millimeter-wave frequencies is of great interest in many applications where simultaneous determination of the complex dielectric properties and thicknesses of multiple layers is desired. Open-ended rectangular waveguide probes, radiating into such structures, are effective tools for this purpose. The technique utilizes a full-wave electromagnetic model that accurately models the complex reflection coefficient as a function of frequency and material properties. While the electromagnetic model assumes an infinite waveguide flange (or ground plane), the measurements are conducted using a finite-sized flange. Consequently, the results of the electromagnetic model and those from measurements may not be sufficiently alike for accurate dielectric property and thickness evaluation. This paper investigates the effect of using an open-ended waveguide with a standard finite-sized flange on the error in evaluating the complex dielectric properties of a composite structure. Additionally, we present the design of a novel flange that markedly reduces this undesired effect by producing very similar electric field properties, at the flange aperture, to those created by an infinite flange. Finally, the efficacy of the design for evaluating the dielectric properties of a layered composite structure is demonstrated as well

Leafy, terminal flower1 and agamous are functionally conserved but do not regulate terminal flowering and floral determinacy in Impatiens balsamina

In Impatiens balsamina a lack of commitment of the meristem during floral development leads to the continuous requirement for a leaf-derived floral signal. In the absence of this signal the meristem reverts to leaf production. Current models for Arabidopsis state that LEAFY (LFY) is central to the integration of floral signals and regulates flowering partly via interactions with TERMINAL FLOWER1 (TFL1) and AGAMOUS (AG). Here we describe Impatiens homologues of LFY, TFL1 and AG (IbLFY, IbTFL1 and IbAG) that are highly conserved at a sequence level and demonstrate homologous functions when expressed ectopically in transgenic Arabidopsis. We relate the expression patterns of IbTFL1 and IbAG to the control of terminal flowering and floral determinacy in Impatiens. IbTFL1 is involved in controlling the phase of the axillary meristems and is expressed in axillary shoots and axillary meristems which produce inflorescences, but not in axillary flowers. It is not involved in maintaining the terminal meristem in either an inflorescence or indeterminate state. Terminal flowering in Impatiens appears therefore to be controlled by a pathway that uses a different integration system than that regulating the development of axillary flowers and branches. The pattern of ovule production in Impatiens requires the meristem to be maintained after the production of carpels. Consistent with this morphological feature IbAG appears to specify stamen and carpel identity, but is not sufficient to specify meristem determinacy in Impatiens